JPH0363467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a power supply device for an AC arc welding machine that performs AC arc welding on aluminum or the like using a switching transistor or the like.

(b) Prior Art As a conventional power supply device for an AC arc welding machine, a power supply unit for an AC arc welding machine has been put into practical use, which once converts commercial power to a high frequency, and then transforms the voltage and shapes the wave into a rectangular wave. A circuit diagram of this power supply device for an AC arc welding machine is shown in FIG. In this power supply device, as shown in the figure, after rectifying and smoothing a three-phase AC power supply 1 using a rectifier circuit 2 and a smoothing capacitor 3, switching transistors 4 and 5 and an output control circuit 6
High frequency switching is performed with high frequency (usually 2~
20KHz). Furthermore, the high frequency output is transformed to several tens to hundreds of volts by the transformer 7, and then the rectifier 8,
9, a smoothing reactor 10 and a smoothing capacitor 11 convert the current into direct current again. After this, switching transistors 12 to 15 and low frequency control circuit 1
6 performs a reverse switching operation to obtain a highly accurate rectangular wave (usually 50 to 100 Hz) welding current. In the figure, 17 is a high-frequency oscillator to facilitate arc ignition at the start of operation when performing TIG welding, etc., and 20 is a current detector, whose detected value is fed back to the output control circuit 6 and output. Constant current control is performed. Furthermore, switching transistors 12 to 15
Generally, protection diodes 21 to 24 are connected in parallel to protect these transistors.

In the above-described power supply device for an AC arc welding machine, since voltage transformation and rectification can be performed at high frequencies, the transformer and reactor can be configured for high frequency use, making it possible to achieve downsizing and cost reduction. Based on this, the current control of the output control circuit 6 can be performed accurately with a fast response speed. Furthermore, while AC arc welding can be performed by switching the switching transistors using the low frequency control circuit 16, there is also the advantage that DC arc welding can be performed by keeping either the switching transistors 12, 15 or 13, 14 in the ON state. be.

(c) Problems to be Solved by the Invention However, in the above power supply device for an AC arc welding machine, if the distance between the power supply device and the base material 19 is long, it is necessary to lengthen the cable attached to the power supply device. If this long cable is attached, the cable may become coiled if the base material is placed near the power supply device. In such a case, the reactor 25 is formed by the cable itself as shown in the figure. Now considering that the switching transistors 14 and 13 are on, the load current is from the switching transistor 14, the reactor 25, the base material 19, and the welding electrode 1.
8. A voltage flows in the path of the high frequency oscillator 17 and the switching transistor 13, and a voltage is generated in the reactor 25 in the direction shown by the solid line in the figure, but at the moment when these switching transistors 14 and 13 turn off. , a voltage indicated by a dotted line in the figure is induced in the reactor 25. Based on this voltage, circulating current i flows through the path of base material 19, welding electrode 18, high frequency oscillator 17, protection diode 21, smoothing capacitor 11, and protection diode 24, and smoothing capacitor 11 is charged. When the switching transistors 12 and 15 turn off from the on state, a circulating current i flows in the same direction, and the capacitor 11 is charged by this circulating current. Therefore, depending on the size of the reactor 25 generated in the cable, a considerably high voltage may be charged to the smoothing capacitor 11, and this voltage may destroy the switching transistors 12-15. For example, when a 20m cable is wound with a diameter of 400mm,
Intact dance is approximately 85μH. When a current of 300A is passed through this cable (when the capacitor is 1000μF), the voltage generated in the reactor 25 will be approximately 123V.

In the conventional power supply device, a high voltage may be generated in the reactor 25 as described above, so the charging voltage of the smoothing capacitor 11 gradually increases during use, and eventually the switching transistor There was a possibility that 12-15 would be destroyed.

The purpose of this invention is to extract only this alternating voltage because the voltage generated when the cable is wound to create a reactor is an alternating voltage that is different from the square wave voltage applied to the load. 1st
An object of the present invention is to provide a power supply device for an AC arc welding machine that feeds back to the smoothing capacitor of the rectifier circuit and prevents the charging voltage of the smoothing capacitor from exceeding a certain level.

(d) Means for solving the problem The present invention provides a first method for rectifying and smoothing an alternating current power source.
a rectifier circuit, a high-frequency conversion circuit that converts a DC voltage to a high frequency, a transformer that transforms the high-frequency voltage, a second rectifier circuit that rectifies the output of the transformer into positive and negative, and the rectifier. It has a smoothing circuit including a smoothing reactor and a smoothing capacitor that smooths the output, and an opening and closing circuit that switches the smoothed output of the smoothing circuit and applies it to the welding electrode and the base material with positive or negative polarity, and the opening and closing circuit alternately In the power supply device for an AC arc welding machine, which includes a switching element that turns on and off and a protection diode therefor, a series circuit of a DC component removal capacitor and a primary winding of a voltage feedback transformer is connected between the output terminals of the switching circuit. In addition, a voltage feedback circuit is provided for rectifying the secondary output voltage of the voltage feedback transformer and feeding it back to the smoothing capacitor of the first rectifier circuit.

(e) Effect In the power supply device for an AC arc welding machine according to the present invention, AC power is once rectified into DC in the first rectifier circuit, and then converted into high frequency in the high frequency conversion circuit. Furthermore, the high frequency voltage is transformed by a transformer, rectified and smoothed by a second rectifier circuit, and output to a switching circuit. In the opening/closing circuit, switching elements alternately turn on and off, converting the current into a low-frequency rectangular wave current, and outputting it to the welding electrode and base metal. When performing AC arc welding, if a reactor part is formed in the cable connecting the base metal and the power supply device, during switching, that is, from positive polarity (or negative polarity) to negative polarity (or positive polarity). ), a voltage is induced in the reactor. The direction of the voltage induced at this time is the direction of the current that was flowing immediately before. Therefore, the polarity of the protection diode connected to the switching element is in the forward direction with respect to the polarity of this induced voltage, and a circulating current flows through the welding electrode, the base material, and the protection diode based on the induced voltage. This circulating current charges the smoothing capacitor of the smoothing circuit. However, since this circulating current flows based on the kick voltage of the reactor, |di/dt| is always positive, unlike the waveform of the load current (rectangular wave). In other words, it changes in an alternating current manner. Therefore, a part of the current based on the induced voltage of the reactor passes through the DC removal capacitor connected between the output terminals of the switching circuit and is applied to the primary winding of the voltage feedback transformer. The secondary winding output voltage of the voltage feedback transformer is rectified by the feedback circuit and fed back to the smoothing capacitor of the first rectifier circuit.

Therefore, a part of the voltage generated in the reactor formed in the cable is returned to the smoothing capacitor of the first rectifier circuit by the feedback circuit, so the circulating current flows and the smoothing capacitor of the smoothing circuit is charged. It cannot be done indefinitely. Therefore, the rise in the charging voltage of the smoothing capacitor can be limited to below the breakdown voltage of the switching element of the switching circuit. When a reactor is formed in the first rectifier and a kick voltage is generated across the reactor, the voltage is fed back to the first rectifier circuit, so that no energy loss occurs.

(f) Embodiment FIG. 1 is a circuit diagram of a power supply device for an AC arc welding machine which is an embodiment of the present invention.

The difference between this embodiment and the power supply device shown in FIG.
A series circuit with the primary winding b is connected, and a high frequency removal capacitor 26c is connected in parallel to the series circuit.
and a rectifier 26 which further configures a feedback circuit between the secondary winding output terminals of the voltage feedback transformer 26b.
d is connected, and its rectified output terminal is connected to the smoothing capacitor 3 of the first rectifying circuit.

Next, the operation will be explained.

When the power is turned on, the AC voltage is first rectified by the first rectifier circuit 2, smoothed by the smoothing capacitor 3, and then switched at a predetermined duty by the switching transistors 4 and 5 of the high frequency conversion circuit. The switching voltage is transformed by transformer 7,
It is rectified by diodes 8 and 9 and sent to a smoothing circuit. Smoothing reactor 10 and smoothing capacitor 1
The output smoothed by 1 is output to a switching circuit having four switching transistors 12 to 15, where it is alternately switched to positive polarity or negative polarity and supplied to a load. In the case of positive polarity, transistors 13 and 14 are turned on. In this positive polarity, the smoothed output is transmitted to the transistor 14, the reactor 25 formed in the cable, the base material 19, the welding electrode 18, the high frequency oscillator 17, and the transistor 13.
flows. Also, when the polarity is negative, transistor 1
2 and 15 are turned on, and the smoothed output is from transistor 1.
2, high frequency oscillator 17, welding electrode 18, base material 1
9, reactor 25, and transistor 15. At the time of arc start, the high frequency oscillator 17 is activated to facilitate transition to the arc state. When an arc occurs, the high frequency oscillator 17 is turned off, and the positive polarity,
Load current flows alternately with negative polarity. The load current is detected by the current detector 20, and the detected value is output to the output control circuit 6. The output control circuit 6 compares the detected value from the current detector 20 with a reference value set by the variable resistor 6a, and controls the switching transistors 4 and 5 based on the magnitude of the error.
Controls the duty of the switching pulse output to the That is, the duty of the switching pulse is controlled so that the detected value and the reference value become equal. By performing this operation, constant current control of the load current (output current) is performed. Further, the low frequency control circuit 16 includes the switching transistor 1
A switching pulse that alternately turns on and off signals 2 to 15 is output, and the switching frequency can be changed by a variable resistor 16a. Such a circuit can be easily constructed using a multivibrator or the like. Output control circuit 6
The frequency of the switching pulses generated by the switching pulse is normally controlled in the range of 2 to 20KHz, and
The frequency of the switching pulses generated at 6 is normally controlled in the range of 50-100Hz.

During arc operation, the voltage induced in the reactor 25 at the time of switching (at the moment of switching from positive polarity to negative polarity or from negative polarity to positive polarity) is applied to the transistor that is about to switch from on to off. The connected protection diode is in the forward direction. Therefore, based on the induced voltage, a circulating current flows through the base material 19, the welding electrode 18, and the high frequency oscillator 17 into the smoothing circuit, and the smoothing capacitor 11 is charged by the current. Since this circulating current flows every time the polarity changes, the charging voltage of the smoothing capacitor 11 tends to gradually increase. However, a part of the current based on the induced voltage of the reactor 25 passes through the DC component removal capacitor 26a and flows to the primary side of the voltage feedback transformer 26b. Therefore, its primary side is excited and a voltage is generated on its secondary side. This voltage is rectifier 2
6d and fed back to the smoothing capacitor 3 of the first rectifier circuit. In addition, the voltage feedback transformer 26d
The winding ratio between the primary side and the secondary side is set to such an extent that the output voltage on the secondary side is approximately equal to the rectified output voltage of the first rectifier circuit.

Due to the above-mentioned effect, the magnitude of the feedback current flowing through the smoothing capacitor 11 becomes extremely small, and it is possible to prevent the charging voltage of the smoothing capacitor 11 from increasing to the extent that it will destroy the switching transistor. In addition, the high frequency removal capacitor 26c
is for removing high frequency components generated during switching.

The fact that a certain amount of voltage is generated on the primary side of the voltage feedback transformer 26b means that a reactor is formed in the cable connected to the base material 19. This reactor causes the charging voltage of the smoothing capacitor to increase as described above, and also slows down the load current. Ideally, the load current is a rectangular wave, but if it is no longer a rectangular wave due to the reactor, the welding current may become insufficient and weld defects may occur. Furthermore, when welding aluminum, there are cases where welding becomes impossible because a sufficient cleaning action cannot be performed when the polarity is negative. In order to avoid such a situation, in the example shown in FIG. 2, the voltage on the primary side of the voltage feedback transformer 26d is rectified and compared with the reference voltage E ₀ by the comparator 31. The voltage on the primary side is the reference voltage
When E exceeds ₀ , the alarm circuit 29 is driven and the speaker 30 emits an alarm sound to the outside. When the alarm sounds in this way, workers nearby can see that the cable is coiled and a reactor is formed. The rolled part can be straightened.

FIG. 3 shows another embodiment of the invention.

In this embodiment, the switching transistors 4 and 5 are connected in a half bridge on the primary side of the transformer 7. Further, the secondary output of the transformer 7 is rectified into positive and negative by the diodes 31 to 34, and the positive rectified output passes through the first smoothing reactor 50.
The negative rectified output passes through the second smoothing reactor 51. The positive output flowing through the first smoothing reactor 50 is connected to the smoothing capacitor 11 via the diode 27.
The charging voltage is applied to the welding electrode 18 and the base material 19 through the first switching transistor 36.
applied in between. Also, a second smoothing reactor 51
The negative current flowing through charges the smoothing capacitor 11, and the charging voltage is applied between the welding electrode 18 and the base material 19 via the second switching transistor 37. In this embodiment, two switching transistors 36 and 37 are used as switching elements of the opening/closing circuit as described above, and each transistor alternately supplies a positive output and a negative output to the load. Low frequency control circuit 16
transmits a switching pulse at a frequency set by the variable resistor 16a to the transistors 36,
This pulse turns each transistor 36 and 37 on and off alternately. 4
4 and 45 are these switching transistors 3
This is a protection diode connected in parallel to 6 and 37. Further, in this embodiment, the first smoothing reactor 5
The iron cores of the smoothing reactor 0 and the second smoothing reactor 51 are the same, and their respective windings are coupled. The direction of the bond is in the opposite direction. For this reason, the first
Due to the induced voltage V1 generated in the L direction in the smoothing reactor 50, the second smoothing reactor 51 has M
A voltage of V2 is induced in the direction. With this configuration, when a voltage of positive polarity is applied to the load, that is, from a state where the switching transistor 36 is on, the voltage is switched to negative polarity, and the first voltage is applied at the timing of the switching. A voltage V1 is generated in the smoothing reactor 50 in the L direction shown in the figure, and induced by this voltage, a voltage V2 is generated in the second smoothing reactor 51 in the M direction. Since this voltage V2 is added to the negative voltage rectified by the diodes 33 and 34 when the polarity changes from positive to negative, the welding electrode 18 and base material 19
A large voltage is applied between them. Therefore, it is possible to prevent the arc from misfiring at this electrode time, and there is an advantage that a stable arc state can be maintained.

A DC removal capacitor 2
6a and the primary winding of the voltage feedback transformer,
A high frequency removal capacitor 26b is connected in parallel to the series circuit. Further, the secondary winding output of the voltage feedback transformer 26b is connected to a rectifier 26d, and its rectified output terminal is connected to the input side of the high frequency conversion circuit.
It is connected to the terminal b. When the voltage across the primary winding of the voltage feedback transformer 26b exceeds a certain level, the output from the secondary winding is rectified, and the smoothing capacitors 3a and 3b on the power supply rectification side are rectified.
will be returned to.

(g) Effects of the Invention According to this invention, even if a reactor component is formed in the coiled state of the cable, it is possible to prevent the charging voltage of the smoothing capacitor from rising above a certain voltage. Therefore, it is possible to prevent the switching transistor in the switching circuit from being destroyed. Further, since the voltage feedback circuit operates to return excess energy stored in the smoothing capacitor to the primary side (smoothing capacitor of the first rectifier circuit), there is an advantage that there is no loss of energy.

[Brief explanation of drawings]

FIG. 1 shows a circuit diagram of an embodiment of the invention. FIG. 2 shows a partial circuit diagram of another embodiment, and FIG. 3 shows a circuit diagram of still another embodiment. Further, FIG. 4 shows a circuit diagram of a conventional power supply device. 12 to 15, 36, 37...Switching elements (switching transistors) of open/close circuits, 21
~24,44,45...Protection diode, 26a
. . . DC component removal capacitor, 26b . . . Voltage feedback transformer, 26d . . . Rectifier (voltage feedback circuit).

Claims (1)

[Scope of Claims] 1. A first rectifier circuit that rectifies and smoothes an AC power source, a high frequency conversion circuit that converts a DC voltage to a high frequency, and a transformer that transforms the high frequency voltage.
a second rectifier circuit that rectifies the output of the transformer into positive and negative; a smoothing circuit that includes a smoothing reactor and a smoothing capacitor that smooth the rectified output; and a smoothing circuit that switches the smoothed output of the smoothing circuit to have positive or negative polarity. A power supply device for an AC arc welding machine, which has a welding electrode and a switching circuit that applies voltage to a base material, and the switching circuit includes a switching element that turns on and off alternately and a protection diode for the switching element, wherein a DC current is applied between the output terminals of the switching circuit. At the same time, the secondary side output voltage of the voltage feedback transformer is rectified and fed back to the smoothing capacitor of the first rectifier circuit. A power supply device for an AC arc welding machine, characterized in that it is provided with a voltage feedback circuit.